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Gypsum
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<p>Gypsum is a soft <a href="/facts/Sulfate_mineral/AQAw1nJg">sulfate mineral</a> composed of <a href="/facts/Calcium_sulfate/mTD8oGaH">calcium sulfate</a> <a href="/facts/Hydrate/dev82l69">dihydrate</a>, with the <a href="/facts/Chemical_formula/hghUtthl">chemical formula</a> CaSO4·2H2O. It is widely mined and is used as a <a href="/facts/Fertilizer/ysh3r6NJ">fertilizer</a> and as the main constituent in many forms of <a href="/facts/Plaster/GG73HRD7">plaster</a>, <a href="/facts/Drywall/hR6CWcVT">drywall</a> and <a href="/facts/Blackboard/sznfTHlD">blackboard</a> or <a href="/facts/Sidewalk_chalk/sR9h1Sl9">sidewalk chalk</a>. Gypsum also <a href="/facts/Crystallization/oCUUG80k">crystallizes</a> as translucent crystals of <a href="/facts/Selenite_(mineral)/ChMIJw4P">selenite</a>. It forms as an <a href="/facts/Evaporite/vNW8fcEy">evaporite</a> mineral and as a <a href="/facts/Mineral_hydration/YJ1NEwVP">hydration</a> product of <a href="/facts/Anhydrite/66QvVbXV">anhydrite</a>. The <a href="/facts/Mohs_scale_of_mineral_hardness/wXBMcVIm">Mohs scale of mineral hardness</a> defines gypsum as hardness value 2 based on <a href="/facts/Scratch_hardness/5V7xkqar">scratch</a> <a href="/facts/Hardness_comparison/zkwUmdLu">hardness comparison</a>. </p><p>Fine-grained white or lightly tinted forms of gypsum known as <a href="/facts/Alabaster/wLAtReg3">alabaster</a> have been used for <a href="/facts/Sculpture/F01q8gtb">sculpture</a> by many cultures including <a href="/facts/Ancient_Egypt/BDsEGK4g">Ancient Egypt</a>, <a href="/facts/Mesopotamia/f0mmbhTK">Mesopotamia</a>, <a href="/facts/Ancient_Rome/cGqIuxPd">Ancient Rome</a>, the <a href="/facts/Byzantine_Empire/njEELXWF">Byzantine Empire</a>, and the <a href="/facts/Nottingham_alabaster/8x0Iw7Rq">Nottingham alabasters</a> of <a href="/facts/Medieval_England/XFS67p7P">Medieval England</a>. </p>